Relationships Between Alveolar Size and Fibre Distribution in a Mammalian Lung Alveolar Duct Model

1997 ◽  
Vol 119 (3) ◽  
pp. 289-297 ◽  
Author(s):  
E. Denny ◽  
R. C. Schroter
Keyword(s):  
Static Pressure ◽  
Collagen Fibre ◽  
Element Model ◽  
Volume Density ◽  
Fibre Volume ◽  
Published Data ◽  
Liquid Interfaces ◽  
Tension Properties ◽  
Alveolar Duct ◽  
Mammalian Lung

A finite element model, comprising an assemblage of tetrakaidecahedra or truncated octahedra, is used to represent an alveolar duct unit. The dimensions of the elastin and collagen fibre bundles, and the surface tension properties of the air-liquid interfaces, are based on available published data. Changes to the computed static pressure-volume behavior with variation in alveolar dimensions and fibre volume densities are characterized using distensibility indices (K). The air-filled lung distensibility (Ka) decreased with a reduction in the alveolar airspace length dimensions and increased with a reduction of total fibre volume density. The saline-filled lung distensibility (Ks) remained constant with alveolar dimensions and increased with decreasing total fibre volume density. The degree of geometric anisotropy between the duct lumen and alveoli was computed over pressure-volume cycles. To preserve broadly isotropic behavior, parenchyma with smaller alveolar airspace length dimensions required higher concentrations of fibres located in the duct and less in the septa in comparison with parenchyma of larger airspace dimensions.

The Mechanical Behavior of a Mammalian Lung Alveolar Duct Model

1995 ◽  
Vol 117 (3) ◽  
pp. 254-261 ◽  
Author(s):  
E. Denny ◽  
R. C. Schroter
Keyword(s):  
Experimental Data ◽  
Mechanical Properties ◽  
Collagen Fiber ◽  
Fiber Bundles ◽  
Published Data ◽  
The Finite Element Method ◽  
Dependent Relationship ◽  
Alveolar Duct ◽  
Mammalian Lung ◽  
Air Liquid Interface

A model for the mechanical properties of an alveolar duct is analyzed using the finite element method. Its geometry comprises an assemblage of truncated octahedral alveoli surrounding a longitudinal air duct. The amounts and distributions of elastin and collagen fiber bundles, modeled by separate stress-strain laws, are based upon published data for dogs. The surface tension of the air-liquid interface is modeled using an area-dependent relationship. Pressure-volume curves are computed that compare well with experimental data for both saline-filled and air-filled lungs. Pressure-volume curves of the separate elastin and collagen fiber contributions are similar in form to the behavior of saline-filled lungs treated with either elastase or collagenase. A comparison with our earlier model, based upon a single alveolus, shows the duct to have a behavior closer to reported experimental data.

Viscoelastic Behavior of a Lung Alveolar Duct Model

1999 ◽  
Vol 122 (2) ◽  
pp. 143-151 ◽  
Author(s):  
E. Denny ◽  
R. C. Schroter
Keyword(s):  
Surface Tension ◽  
Tidal Volume ◽  
Viscoelastic Behavior ◽  
Surface Tension Force ◽  
Element Model ◽  
Lung Parenchyma ◽  
Oscillatory Behavior ◽  
Published Data ◽  
Elastic Model ◽  
Alveolar Duct

A study is conducted into the oscillatory behavior of a finite element model of an alveolar duct. Its load-bearing components consist of a network of elastin and collagen fibers and surface tension acting over the air–liquid interfaces. The tissue is simulated using a visco-elastic model involving nonlinear quasi-static stress–strain behavior combined with a reduced relaxation function. The surface tension force is simulated with a time- and area-dependent model of surfactant behavior. The model was used to simulate lung parenchyma under three surface tension cases: air-filled, liquid-filled, and lavaged with 3-dimethyl siloxane, which has a constant surface tension of 16 dyn/cm. The dynamic elastance Edyn and tissue resistance Rti were computed for sinusoidal tidal volume oscillations over a range of frequencies from 0.16–2.0 Hz. A comparison of the variation of Edyn and Rti with frequency between the model and published experimental data showed good qualitative agreement. Little difference was found in the model between Rti for the air-filled and lavaged models; in contrast, published data revealed a significantly higher value of Rti in the lavaged lung. The absence of a significant increase in Rti for the lavaged model can be attributed to only minor changes in the individual fiber bundle resistances with changes in their configuration. The surface tension was found to make an important contribution to both Edyn and Rti in the air-filled duct model. It was also found to amplify any existing tissue dissipative properties, despite exhibiting none itself over the small tidal volume cycles examined. [S0148-0731(00)00502-1]

A model for mechanical structure of the alveolar duct

1982 ◽  
Vol 52 (4) ◽  
pp. 1064-1070 ◽  
Author(s):  
T. A. Wilson ◽  
H. Bachofen
Keyword(s):  
Surface Tension ◽  
Lung Volume ◽  
Published Data ◽  
Scanning Electron Micrographs ◽  
Fiber System ◽  
Lung Capacity ◽  
Alveolar Duct ◽  
Tissue System ◽  
Line Elements ◽  
Air Liquid Interface

The appearance of the microstructure of the lung as revealed in transmission and scanning electron micrographs of perfusion-fixed air- and saline-filled lungs suggests the following model for the structure of the alveolar duct. There are two networks of force-bearing elements. The first is an interdependent part of the peripheral connective tissue system that starts from the pleura and extends into the interlobar and interlobular fissures. At the sublobular level, its geometry is not yet fully clear. This network is extended by changes in lung volume and is insensitive to surface tension. The second network is composed of the line elements that form the rims of the alveolar openings. This network is the terminal part of the axial fiber system that surrounds bronchi, bronchioli, and arteries. The line elements of this network are extended by the outward force of surface tension. The two-dimensional alveolar walls that form the alveoli are negligible mechanical components except as platforms for surface tension at the air-liquid interface. An analysis of the mechanics of this model yields relations among surface area, recoil pressure, lung volume, and surface tension that are consistent with published data for lung volumes below 80% of total lung capacity.

Ultrastructure of Aerobic Muscle in Antarctic Fishes may Contribute to Maintenance Of Diffusive Fluxes

1990 ◽  
Vol 150 (1) ◽  
pp. 205-220 ◽  
Author(s):  
RICHARD L. LONDRAVILLE ◽  
BRUCE D. SIDELL
Keyword(s):  
Muscle Metabolism ◽  
Antarctic Fish ◽  
Oxygen Demand ◽  
Capillary Density ◽  
Volume Density ◽  
Active Species ◽  
Published Data ◽  
Diffusion Distance ◽  
Capillary Length ◽  
Diffusive Fluxes

Quantitative ultrastructural analyses were performed on red (oxidative) and white (glycolytic) skeletal muscles from two species of antarctic fish to identify features of subcellular structure that may be related to muscle metabolism at cold body temperature. Trematomus newnesi (Boulenger) is an active pelagic species and Notothenia gibberifrons (Lönnberg) is a sluggish bottom-dweller. White fibres of both species are poorly vascularized [capillary density, NA(c,f), for T. newnesi 73.9±11.3mm−2; for N. gibberifrons is 76.0±14.1mm−2], and have low percentages of cell volume occupied by mitochondria [volume density, Vv(mit,f), for T. newnesi is 0.014±0.005; for N. gibberifrons is 0.006±0.003]. Ultrastructure of oxidative fibres in both species resembles that of cold-acclimated temperate-zone fishes. Mitochondrial volume densities of red fibres reflect differences in ecotype between species [Vv(mit,f) for T. newnesi is 0.348±0.012; for N. gibberifrons is 0.249±0.007]. The less clustered array of mitochondria in oxidative fibres of T. newnesi compared with N. gibberifrons may support an equivalent flux of aqueous metabolites between mitochondrial and cytoplasmic compartments, despite a greater mean intracellular diffusion distance (τh) between these compartments in T. newnesi than in N. gibberifrons (τh=1.05±0.07μm and 0.77±0.06μm, respectively). Although Vv(mit.)) is higher in red fibres of the active species, capillary supply is less extensive [capillary length density, Jv(c,f), for T. newnesi is 481.3±49.0mm mm−3; N. gibberifrons is 696.3±33.7mm mm−3] and the maximal diffusion-distance for oxygen is greater in T. newnesi than in N. gibberifrons (Krogh's radius, R=26.3±1.64μm and 21.5±0.51μm, respectively). A mismatch appears to exist between oxygen supply [Jv(c,f)] and oxygen demand [Vv(mit,f)] in T. newnesi red fibres in view of published data for other fishes. The twofold higher volume density of lipid [Vv(lip,f)] in T. newnesi compared with N. gibberifrons may resolve this paradox [Vv(lip,f) is 0.026±0.002 and 0.012±0.004, respectively]. Because oxygen is at least four times more soluble in lipid than in aqueous cytoplasm, lipid may enhance oxygen flux through oxidative muscle and play a role similar to myoglobin in these myoglobin-poor fishes.

FEBio finite element model of a pediatric cervical spine

2021 ◽  
pp. 1-7
Author(s):  
Sean M. Finley ◽  
J. Harley Astin ◽  
Evan Joyce ◽  
Andrew T. Dailey ◽  
Douglas L. Brockmeyer ◽  
...  
Keyword(s):  
Finite Element ◽  
Cervical Spine ◽  
Finite Element Model ◽  
Material Properties ◽  
Surgical Simulation ◽  
Element Model ◽  
Axial Stiffness ◽  
Published Data ◽  
Axial Tension ◽  
Flexion Extension

OBJECTIVE The underlying biomechanical differences between the pediatric and adult cervical spine are incompletely understood. Computational spine modeling can address that knowledge gap. Using a computational method known as finite element modeling, the authors describe the creation and evaluation of a complete pediatric cervical spine model. METHODS Using a thin-slice CT scan of the cervical spine from a 5-year-old boy, a 3D model was created for finite element analysis. The material properties and boundary and loading conditions were created and model analysis performed using open-source software. Because the precise material properties of the pediatric cervical spine are not known, a published parametric approach of scaling adult properties by 50%, 25%, and 10% was used. Each scaled finite element model (FEM) underwent two types of simulations for pediatric cadaver testing (axial tension and cardinal ranges of motion [ROMs]) to assess axial stiffness, ROM, and facet joint force (FJF). The authors evaluated the axial stiffness and flexion-extension ROM predicted by the model using previously published experimental measurements obtained from pediatric cadaveric tissues. RESULTS In the axial tension simulation, the model with 50% adult ligamentous and annulus material properties predicted an axial stiffness of 49 N/mm, which corresponded with previously published data from similarly aged cadavers (46.1 ± 9.6 N/mm). In the flexion-extension simulation, the same 50% model predicted an ROM that was within the range of the similarly aged cohort of cadavers. The subaxial FJFs predicted by the model in extension, lateral bending, and axial rotation were in the range of 1–4 N and, as expected, tended to increase as the ligament and disc material properties decreased. CONCLUSIONS A pediatric cervical spine FEM was created that accurately predicts axial tension and flexion-extension ROM when ligamentous and annulus material properties are reduced to 50% of published adult properties. This model shows promise for use in surgical simulation procedures and as a normal comparison for disease-specific FEMs.

Pipeline Dent Management Program

2002 ◽  
Author(s):  
Scott D. Ironside ◽  
L. Blair Carroll
Keyword(s):  
Finite Element ◽  
Oil And Gas ◽  
Selection Process ◽  
Element Model ◽  
Field Trials ◽  
Management Program ◽  
Operating Conditions ◽  
Published Data ◽  
Element Analysis ◽  
The Past

Enbridge Pipelines Inc. operates the world’s longest and most complex liquids pipeline network. As part of Enbridge’s Integrity Management Program In-Line Inspections have been and will continue to be conducted on more than 15,000 km of pipeline. The Inspection Programs have included using the most technologically advanced geometry tools in the world to detect geometrical discontinuities such as ovality, dents, and buckles. During the past number of years, Enbridge Pipelines Inc. has been involved in developing a method of evaluating the suitability of dents in pipelines for continued service. The majority of the work involved the development of a method of modeling the stresses within a dent using Finite Element Analysis (FEA). The development and validation of this model was completed by Fleet Technology Limited (FTL) through several projects sponsored by Enbridge, which included field trials and comparisons to previously published data. This model combined with proven fracture mechanics theory provides a method of determining a predicted life of a dent based on either the past or future operating conditions of the pipeline. CSA Standard Z662 – Oil and Gas Pipeline Systems provides criteria for the acceptability of dents for continued service. There have been occurrences, however, where dents that meet the CSA acceptability criteria have experienced failure. The dent model is being used to help define shape characteristics in addition to dent depth, the only shape factor considered by CSA, which contribute to dent failure. The dent model has also been utilized to validate the accuracy of current In-Line Inspection techniques. Typically a dent will lose some of its shape as the overburden is lifted from the pipeline and after the indentor is removed. Often there can be a dramatic “re-rounding” that will occur. The work included comparing the re-rounded dent shapes from a Finite Element model simulating the removal of the constraint on the pipe to the measured dent profile from a mold of the dent taken in the field after it has been excavated. This provided a measure of the accuracy of the tool. This paper will provide an overview of Enbridge’s dent management program, a description of the dent selection process for the excavation program, and a detailed review of the ILI validation work.

scholarly journals In silico stress fibre content affects peak strain in cytoplasm and nucleus but not in membrane for uniaxial substrate stretch

2019 ◽  
Author(s):  
Tamer Abdalrahman ◽  
Neil H. Davies ◽  
Thomas Franz
Keyword(s):  
Elastic Modulus ◽  
In Silico ◽  
Focal Adhesions ◽  
Element Model ◽  
Homogenization Method ◽  
Fibre Volume ◽  
Fibre Content ◽  
Peak Strain ◽  
Stress Fibre ◽  
A Cell

AbstractExisting in silico models for single cell mechanics feature limited representations of cytoskeletal structures that contribute substantially to the mechanics of a cell. We propose a micromechanical hierarchical approach to capture the mechanical contribution of actin stress fibres. For a cell-specific fibroblast geometry with membrane, cytoplasm and nucleus, the Mori-Tanaka homogenization method was employed to describe cytoplasmic inhomogeneities and constitutive contribution of actin stress fibres. The homogenization was implemented in a finite element model of the fibroblast attached to a substrate through focal adhesions. Strain in cell membrane, cytoplasm and nucleus due to uniaxial substrate stretch was assessed for different stress fibre volume fractions and different elastic modulus of the substrate. A considerable decrease of the peak strain with increasing stress fibre content was observed in cytoplasm and nucleus but not the membrane, whereas the peak strain in cytoplasm, nucleus and membrane increased for increasing elastic modulus of the substrate.

scholarly journals Thermal conductivity of textile reinforcements for composites

2018 ◽  
Vol 1 ◽  
pp. 251522111775115 ◽  
Author(s):  
Yue El-Hage ◽  
Simon Hind ◽  
François Robitaille
Keyword(s):  
Thermal Conductivity ◽  
Carbon Fibre ◽  
Volume Fraction ◽  
Fibre Volume Fraction ◽  
Three Dimensional ◽  
Fibre Volume ◽  
Published Data ◽  
Manufacturing Processes ◽  
Composites Manufacturing ◽  
The Relationship

Thermal conductivity data for dry carbon fibre fabrics are required for modelling heat transfer during composites manufacturing processes; however, very few published data are available. This article reports in-plane and through-thickness thermal conductivities measured as a function of fibre volume fraction ( Vf) for non-crimp and twill carbon reinforcement fabrics, three-dimensional weaves and reinforcement stacks assembled with one-sided carbon stitch. Composites made from these reinforcements and glass fibre fabrics are also measured. Clear trends are observed and the effects of Vf, de-bulking and vacuum are quantified along with orthotropy ratios. Limited differences between the conductivity of dry glass and carbon fibre fabrics in the through-thickness direction are reported. An unexpected trend in the relationship between that quantity and Vf is explained summarily through simple simulations.

scholarly journals The Off-Axis IBII Test for Composites

2020 ◽  
Author(s):  
S. Parry ◽  
L. Fletcher ◽  
F. Pierron
Keyword(s):  
Shear Modulus ◽  
Strain Rate ◽  
High Strain ◽  
Volume Fraction ◽  
Fibre Volume Fraction ◽  
Fibre Volume ◽  
Published Data ◽  
Shear Moduli ◽  
Test Methodology ◽  
Split Hopkinson

Abstract Composite components regularly experience dynamic loads in service. Despite this, it is still difficult to obtain accurate mechanical properties of composite materials under high strain rate conditions. In this study, a new application of the Image-Based Inertial Impact (IBII) test methodology was developed, to generate an accurate in-plane transverse and shear moduli dataset from unidirectional (UD) off-axis composite specimens. The obtained dataset was consistent across different sample configurations, where results from the UD45$$^{\circ }$$ ∘ off-axis specimens agreed well with the UD90$$^{\circ }$$ ∘ values. Validation of the shear modulus identification was also undertaken by comparing the results from the UD90$$^{\circ }$$ ∘ and UD45$$^{\circ }$$ ∘ specimens with a multi-directional (MD) configuration. Here, it was found that MD±45$$^{\circ }$$ ∘ specimen shear modulus values where marginally lower than that from the UD specimens, in accordance with the lower fibre volume fraction of the MD laminate. Low strain rate sensitivities in the $$0.5-2\times$$ 0.5 - 2 × 10$$^{3}$$ 3  $$\hbox {s}^{-1}$$ s - 1 regime evidenced in this work suggest previously published data (often from split-Hopkinson bar tests) may include both a material and system i.e. testing apparatus response.

A Three-Dimensional Dynamic Finite Element Model of the Prosthetic Knee Joint: Simulation of Joint Laxity and Kinematics

2005 ◽  
Vol 219 (6) ◽  
pp. 415-424 ◽  
Author(s):  
M Barink ◽  
A van Kampen ◽  
M de Waal Malefijt ◽  
N Verdonschot
Keyword(s):  
Finite Element ◽  
Knee Joint ◽  
Finite Element Model ◽  
Mathematical Formulation ◽  
Three Dimensional ◽  
Element Model ◽  
Joint Kinematics ◽  
Published Data ◽  
Dynamic Finite Element ◽  
Flexion Extension

For testing purposes of prostheses at a preclinical stage, it is very valuable to have a generic modelling tool, which can be used to optimize implant features and to avoid poor designs being launched on to the market. The modelling tool should be fast, efficient, and multipurpose in nature; a finite element model is well suited to the purpose. The question posed in this study was whether it was possible to develop a mathematically fast and stable dynamic finite element model of a knee joint after total knee arthroplasty that would predict data comparable with published data in terms of (a) laxities and ligament behaviour, and (b) joint kinematics. The soft tissue structures were modelled using a relatively simple, but very stable, composite model consisting of a band reinforced with fibres. Ligament recruitment and balancing was tested with laxity simulations. The tibial and patellar kinematics were simulated during flexion-extension. An implicit mathematical formulation was used. Joint kinematics, joint laxities, and ligament recruitment patterns were predicted realistically. The kinematics were very reproducible and stable during consecutive flexion-extension cycles. Hence, the model is suitable for the evaluation of prosthesis design, prosthesis alignment, ligament behaviour, and surgical parameters with respect to the biomechanical behaviour of the knee.

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